1. Field of the Invention
The present invention relates to an all solid-state secondary battery, inorganic solid electrolyte particles, a solid electrolyte composition, an electrode sheet for a battery, and a method for manufacturing an all solid-state secondary battery.
2. Description of the Related Art
At present, in a number of versatile lithium ion batteries, an electrolytic solution is used. Attempts are underway to substitute this electrolytic solution with a solid electrolyte so as to constitute lithium ion batteries with only solid materials. Among these attempts, techniques of using an inorganic solid electrolyte have advantages of reliability and stability during use. As electrolytic solutions that are used in lithium ion secondary batteries, flammable materials such as carbonate-based solvents are applied. Therefore, a variety of countermeasures are being employed; however, still, there is a demand for additional countermeasures for overcharging and the like. A solution to this demand is all solid-state secondary batteries in which a non-flammable inorganic compound is used as the electrolyte. Inorganic solid electrolytes also have an advantage of, generally, exhibiting a stronger ion-conducting property than high-molecular-weight electrolytes.
Another advantage of all solid-state secondary batteries is their suitability for an increase in the energy density by means of electrode stacking. Specifically, electrodes and electrolytes can be directly arranged and serialized in batteries. At this time, metal packages for sealing battery cells and copper lines or busbars for connecting the battery cells may not be provided, and thus it is possible to significantly increase the energy density of batteries. In addition, favorable compatibility with positive electrode materials capable of increasing the potential and the like are also said to be still another advantage.
Due to the respective advantages described above, development of all solid-state secondary batteries as next-generation lithium ion secondary batteries actively proceeds (NEDO technical development organization, fuel batteries and hydrogen technical development department, electricity storage technical development division “NEDO secondary battery technical development roadmap 2013” (August 2013)). In all solid-state secondary batteries, particularly, inorganic solid electrolyte layers are members that are not included in liquid-type batteries or high-molecular-weight-type batteries, and development of inorganic solid electrolyte layers is highly expected. Solid electrolyte layers are generally molded by heating and pressurizing electrolyte materials applied to the solid electrolyte layers together with a binder and the like. In such a case, the joint state between the solid electrolyte layers is turned from point contact into surface contact, and grain boundary resistivity is decreased, whereby impedance can be decreased.
There are examples in which the particle diameters of inorganic solid electrolyte particles that are added to solid electrolyte layers and the like are appropriately adjusted in order to improve battery performance. For example, in W02011/105574A, attempts are made to reduce coating unevenness or internal resistance by setting the average particle diameter and the 90% cumulative particle diameter of sulfide glass made up of Li2S and P2S5. In JP5445527B, dibutyl ether is added to a coarse material made up of Li2S and P2S5 and the mixture is milled, whereby it is possible to increase the collection ratio and maintain the ion conductivity.